check whether freeze is due to booster shared lock being held by the …

…SingleRowPredictor

src/c_api.cpp

@@ -121,7 +121,7 @@ struct SingleRowPredictor {
              int predict_type,
              Boosting *boosting,
              int start_iter,
-             int num_iter) : booster_shared_lock(booster_mutex), config(Config::Str2Map(parameters)), data_type(data_type), num_cols(num_cols), single_row_predictor_inner(predict_type, boosting, config, start_iter, num_iter) {
+             int num_iter) : config(Config::Str2Map(parameters)), data_type(data_type), num_cols(num_cols), single_row_predictor_inner(predict_type, boosting, config, start_iter, num_iter), booster_mutex(booster_mutex) {
     if (!config.predict_disable_shape_check && num_cols != boosting->MaxFeatureIdx() + 1) {
       Log::Fatal("The number of features in data (%d) is not the same as it was in training data (%d).\n"\
                  "You can set ``predict_disable_shape_check=true`` to discard this error, but please be aware what you are doing.", num_cols, boosting->MaxFeatureIdx() + 1);
@@ -131,17 +131,14 @@ struct SingleRowPredictor {
   void Predict(std::function<std::vector<std::pair<int, double>>(int row_idx)> get_row_fun,
                double* out_result, int64_t* out_len) const {
     UNIQUE_LOCK(single_row_predictor_mutex)
+    yamc::shared_lock<yamc::alternate::shared_mutex> booster_shared_lock(booster_mutex);
 
     auto one_row = get_row_fun(0);
     single_row_predictor_inner.predict_function(one_row, out_result);
 
     *out_len = single_row_predictor_inner.num_pred_in_one_row;
   }
 
- private:
-  // Prevent the booster from being modified while we have a predictor relying on it
-  yamc::shared_lock<yamc::alternate::shared_mutex> booster_shared_lock;
-
  public:
   Config config;
   const int data_type;
@@ -150,6 +147,9 @@ struct SingleRowPredictor {
  private:
   SingleRowPredictorInner single_row_predictor_inner;
 
+  // Prevent the booster from being modified while we have a predictor relying on it during prediction
+  yamc::alternate::shared_mutex *booster_mutex;
+
   // If several threads try to predict at the same time using the same SingleRowPredictor
   // we want them to still provide correct values, so the mutex is necessary due to the shared
   // resources in the predictor.